Refrigerated containers, or “reefer containers”, are used to transport a vast range of different commodities which are required to be transported under specific conditions.
Cargo shippers typically specify a carriage temperature for their product to be carried under. For example a cargo of frozen tuna may have a carriage temperature set point of −25° C. specified. Allowable deviations from the set-point carriage temperature are normally also specified. The deviations may be in the range of e.g. +/−2.0° C. or even more.
Chilled cargoes, such as fruit, are often required to be carried under more stringent carriage criteria's. For example, chilled cargoes may have a carriage temperature set point of e.g. +1.0° C. specified, with an allowable deviation of only +/−0.5° C.
Even short periods wherein a refrigerated container is left without power may cause the temperature of chilled cargoes to deviate outside the allowable limits, or carriage criteria's, giving rise to potential claims for damage to the cargo.
Some national food safety authorities have requirements as to the maximum period of time that a container may be left without power. For example, when the container is transferred from a terminal stack to a truck for delivery, it may be required that the container is off-power for no more than e.g. 45 minutes regardless of whether the cargo temperature actually is maintained within specified limits.
Some commodities, such as ice cream, are not harmed if the cargo temperature is maintained several degrees lower or higher than the specified carriage temperature, for example −25° C. instead of −20° C., i.e. such cargoes may be specified to be transported under a relatively broad carriage criterion.
U.S. Pat. No. 4,896,277 A discloses a method of mapping addresses of a plurality of refrigerated containers having remote monitoring units (RMUs) connected to a power line carrier based monitoring system which includes a master monitoring unit (MMU). The method adapts to the size of the expected number of containers to be mapped by any mapping command, to reduce the overall time to map either a large or small number of containers.
U.S. Pat. No. 4,885,564 A discloses a power line carrier communication system for monitoring refrigerated containers. The system includes a master monitoring unit and a first power line interface which interchange messages in a first format. The first power line interface translates the first format to a second format suitable for power line environment, and messages in the second format are applied to a power line. Remote monitoring units receive the messages from the power line, and they return messages to the power line containing status data relative to refrigerated containers. The second format includes a message starting preamble having a duration and logic level which is not duplicated by normal operation of the apparatus, enhancing the probability of proper message synchronization and reception over noisy power line environments.
US 2002099567 A discloses an apparatus and method for providing shipment information, including a memory device for storing shipment information, a processor for processing at least one of a request and a prompt to provide shipment information, wherein the processor processes the information contained in the memory device, and further wherein the processor generates a delivery message, wherein the delivery message contains information regarding at least one of a shipment description, contents of a shipment, a description of a shipment's contents, the value of a shipment, an shipment invoice, a shipment packing slip, and a shipment bill, and an output device for at least one of outputting, displaying, and printing, information contained in the delivery message.
US 2007040647 A discloses a unit and system for remote monitoring and controlling of various conditions in a container during cargo transport. The system includes a local wireless or cable (wired) network with a local station and access points positioned in the vicinity of location of containers, a remote central station connected with the Internet and a container-mounted means for monitoring and control of reefer equipment, each of which includes a processor and a transceiver of wireless local communication, a GPS-receiver and a transceiver of cellular communication. The processor is connected to the controller of the reefer equipment, while the transceiver of wireless local communication is made so that the creation of Personal Area Network (PAN) with mobile electronic devices (e.g., Notebook, Pocket PC, PDA) is possible, and establishment of wireless communication with a communication gateway of the said local network is also possible.